When Maguire enters the police car after climbing out of the river his clothes are soaking wet, but a few minutes later he gets out of the car and his clothes appear to be dry.
The liner docks at Tilbury and then the tug heads down stream. There is a conversation on a London Bridge between an Inspector and a PC about it heading downstream and watching for it but Tilbury is miles from the centre of London and there are no bridges from there downstream to the Channel.